The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a magnetic recording head with a writer portion having a high field gradient and cross-track field uniformity.
In an electronic data storage and retrieval system, a transducing head typically includes a writer for storing magnetically-encoded information on a magnetic disc and a reader for retrieving that magnetically-encoded information from the magnetic disc. The reader typically has two shields and a magnetoresistive (MR) sensor positioned between the shields. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. This change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
The writer portion typically consists of a top and a bottom pole, which are separated from each other at an air bearing surface of the writer by a gap layer, and which are connected to each other at a region distal from the air bearing surface by a back gap closer or back via. Positioned between the top and bottom poles are one or more layers of conductive coils encapsulated by insulating layers. The writer portion and the reader portion are often arranged in a merged configuration in which a shared pole serves as both the top shield in the reader portion and the bottom pole in the writer portion.
To write data to the magnetic media, an electric current is caused to flow through the conductive coils to thereby induce a magnetic field across the write gap between the top and bottom poles. By reversing the polarity of the current through the coils, the polarity of the data written to the magnetic media is also reversed. Because the top pole is generally the trailing pole of the top and bottom poles, the top pole is used to physically write the data to the magnetic media. Accordingly, it is the top pole that defines the track width of the written data. More specifically, the track width is defined by the width of the top pole at the air bearing surface.
In magnetic recording, it is desirable to improve the areal density at which information can be recorded and reliably read. This desire has led to a trend toward shorter bit length along a magnetic recording track and a shrinking track width. Narrow track widths are achieved by use of narrow pole tips at an air bearing surface (ABS) of the head. However, a narrower pole tip causes in a weakening of fringing magnetic fields in the gap layer that write data to the magnetic medium. This results in inconsistent writer performance.
One possibility for improving the strength of the gap fringing fields at the magnetic medium is to reduce the spacing between the writer and the medium, thereby bringing the stronger fringing fields at the pole tip closer to the medium. However, as pole tips continue to decrease in size (and the strength of gap fringing fields correspondingly decreases), it becomes increasingly difficult to bring the writer closer to the medium while maintaining a sufficient fly height above the medium. Another possibility is to increase the gap fringing field strength by making the poles out of a material with a higher magnetic saturation moment. While this may improve the gap fringing field strength, the level of improvement is limited by the physics of the materials available. Thus, there is a need for a writer having improved fringing magnetic fields at the write gap.